1. Technical Field
The present invention relates to a semiconductor device and a method of manufacturing the same, particularly to the semiconductor device which has an insulating interlayer and uses a Cu (copper) interconnect and the method of manufacturing the same.
2. Related Art
In recent semiconductor devices represented by a 65-nm node generation, delay of signal propagation in an interconnect is known as a rate-controlling factor in device operation. A delay constant at the interconnect is expressed by a product of interconnect resistance and capacitance among the interconnect. Therefore, in order to increase speed of the device operation by decreasing the interconnect resistance and capacitance among the interconnect, a material (hereinafter referred to as “low dielectric constant material”) having a specific dielectric constant smaller than that of SiO2 is used as the material for the insulating interlayer, and Cu (copper) having smaller specific resistance is being used as the interconnect material.
A Cu multi-layer interconnect is frequently formed by a damascene process.
FIG. 11 is a process cross-sectional view showing a main part of the damascene process.
Namely, as shown in FIG. 11A, first an insulating interlayer 220 made of the low dielectric constant material is formed on a base substance 200 such as a silicon (Si) substrate. Then, as shown in FIG. 11B, an opening H is made in the insulating interlayer 220. The opening H has a role of an interconnect trench for an interconnect layer or a via hole for via. Then, as shown in FIG. 11C, a barrier metal layer 210 is formed in an inner wall of the opening H. As shown in FIG. 11D, an opening H is filled with a Cu layer 300 as the interconnect material. At this point, in many cases where an opening H is filled with the Cu layer 300, Cu is deposited in a thin-film shape by a physical vapor deposition (PVD) method, an opening H is filled with the Cu layer 300 by electrolytic plating method that uses the Cu thin film as a cathode electrode.
In the damascene process, a filled structure shown in FIG. 11D is formed by removing a barrier metal 240 and the Cu layer 300, deposited outside the opening H, by chemical mechanical polishing (CMP) after the barrier metal layer 210 and the Cu layer are deposited.
In this case, the barrier metal layer 210 prevents Cu diffusion into the base substance 200 such as the silicon substrate, improves adhesiveness between the insulating interlayer 220 and the Cu layer 300, and prevents oxidation of the Cu layer 300.
In the barrier metal layer 210, it is difficult that compatibility between the diffusion barrier properties and the adhesiveness. Therefore, in the present circumstances, the barrier metal layer 210 is formed by combination of an amorphous film and a crystalline film. Specifically, the barrier metal layer 210 is formed by a multilayered film including an amorphous film of TaN (tantalum nitride) film with no crystal grain boundary which becomes a high speed diffusion channel and a crystalline Ta film having the adhesiveness to Cu.
Currently one of the most studied techniques as a method of forming the barrier metal is the physical vapor deposition (PVD) method. However, because the PVD method has a worse step coverage, a thickness of a side wall portion is decreased when compared with the thickness of a bottom portion in the interconnect trench or the via hole. In order to decrease the interconnect resistance, it is desirable that the barrier metal is thinned. However, in the PVD method, it is difficult that the thin film is conformaly formed, so that another technique is required in order to form the barrier metal having the thickness of not more than 10 nm.
Therefore, it is demanded that the barrier metal is formed by a chemical vapor deposition (CVD) method. In the CVD method, thin film is easily formed with the good step coverage when compared with the PVD method. Recently the barrier metal is being developed by an atomic layer deposition (ALD) method (or atomic layer chemical vapor deposition (ALCVD) method). The ALD method is of a kind of the CVD method. In the ALD method, when compared with the conventional CVD method, the conformal film is easily obtained with the good step coverage. As one cycle of a depositing procedure of the ALD method, after a first raw material containing an element A is saturation-adsorbed on the substrate, a second raw material containing an element B is supplied to the substrate to react with the first raw material saturation-adsorbed on the substrate, which forms a compound AB. The layer consisting of compound AB having the desired thickness is formed by repeating the above cycle by the predetermined number of times.
When a complicated pattern is formed by CVD method, generally the higher step coverage is obtained in reaction rate-controlling in which a deposition rate is determined by reaction of the raw material on the substrate rather than in supply rate-controlling in which the deposition rate is determined by the supply of the raw material.
Because a deposition principle is the reaction rate controlling in the ideal ALD method, the ALD method is excellent in the step coverage properties and the uniformity of the film thickness when compared with the conventional CD method. In the ALD method, the saturation adsorption is utilized, so that the thickness formed in one cycle is kept constant and thickness controllability is excellent. Further, film composition uniformity is also excellent because the composition is determined by the number of valences of the first raw material and the second raw material.
The barrier metal formed by the ALD method is used in the thin film while the thickness is about several nanometers, so that anitride of high melting point metal which is non-solid-soluble in Cu is used as the material for the barrier metal such that high diffusion barrier properties are obtained. TaN, TaCN, WN, WCN, and TiN can be cited as examples of the barrier metal formed by the ALD method. These materials are formed by performing reduction and nitriding to a metallic compound such as an organometallic compound and a metallic halide with a nitrogen compound such as NH3. These films often have the high resistance. In order to improve the high resistance properties, a method of reducing resistivity of the film by performing plasma treatment to increase density is disclosed (see Japanese Laid-open patent publication NO. 2002-151437).
The barrier metal formed by the ALD method is excellent in the diffusion barrier properties of Cu while the barrier metal has the low adhesiveness. As described above, currently the combination of the amorphous film and the crystalline film is used in order that the diffusion barrier properties are compatible with the adhesiveness in the barrier metal. However, in the ALD method, since the film formation is performed by the saturation adsorption mechanism, it is easy to stably obtain the given composition and the crystalline film while it is difficult to obtain the different compositions and the crystalline film.
A method of forming high melting point metal silicide nitride by mixing silicon is proposed as the technique of improving the adhesiveness. In the ALD method, the following method can be considered as the method of forming the silicide nitride.
(1) the method in which the reduction and the nitriding are performed with the nitrogen compound such as NH3 after the metallic compound and the silicon compound are simultaneously supplied and saturation-adsorbed onto the substrate,
(2) the method in which the reduction and nitriding are performed to the metallic compound to perform the reduction and silicification with the silicon compound, and
(3) the method in which the reduction and the silicification of the metallic compound are performed with SiH4 or the like to perform the reduction and the nitriding of the metallic compound.
However, because a temperature at which the metallic compound is saturation-adsorbed differs from a temperature at which the silicon compound is saturation-adsorbed, in the methods described in (1) and (2), it is difficult to select the raw material. Further, in the method described in (3), there is a concern that impurities such as organic materials and halogens and the like remain due to inadequacy of reduction power of SiH4.
Therefore, the semiconductor device which includes the barrier metal having the high adhesiveness and diffusion barrier properties and the method of manufacturing the semiconductor device are demanded.